Does warcraftlogs create its percent performance against all difficulties?

If so, then the low percents most of us have make a lot more sense for Ursoc. Normal Ursoc would be a majority of the kills and there is much much less movement required. Not to mention time spent just out of range to be in the charge, but not the miasma.

Remember, this is only ranking you amongst those that use warcraftlogs. There are other log sites and not everybody even logs.
I don't have numbers, but I would bet less than 50% of all players log. Typically it is the more hardcore guilds/raiders so this is a comparison to the top X percent of people in the game?